1. Field of the Invention
The subject invention relates generally to the treatment of wastewater and sewage with micro-organisms in the presence of oxygen typically supplied as air or some other source of oxygen, and relates more particularly to aerobically treating relatively small quantities of wastewater and sewage, such as that associated with single family homes, small apartment buildings, small office buildings and the like.
2. Description of Related Art
Ordinary domestic wastewater is comprised of solid materials such as human waste, food scraps, oils, soaps and chemicals. These solid materials must be adequately treated to eliminate health risks, disease control problems, and environmental damage.
The solid materials contained in domestic wastewater typically contain organic substances that are biodegradable under certain conditions, which explains why some wastewater treatment systems employ the process of biodegradation to improve the quality of domestic waste. Optimum biodegradation of domestic waste can be achieved through a process which typically includes the steps of finely dividing the solid materials suspended in the wastewater with some form of agitation, homogeneously mixing the finely divided materials with the liquid wastewater, and then aerating the mixture so as to promote the growth of aerobic bacteria which consumes the wastes. This series of biodegradation steps has been accomplished in small above ground systems and smaller below ground systems where the steps are typically combined into a single stage to minimize the size of the system.
One disadvantage with the small single stage system is that combining the steps of dividing, mixing, and aerating the domestic waste in a single stage prevents the aerobic bacteria from efficiently and effectively consuming the waste. The oxygen which is vital to aerobic activity only gets a single pass at the bacteria contained inside the system, which inevitably leads to inefficient and ineffective operation. The low efficiency and effectiveness usually results in an outflow that contains dissolved and suspended materials which are only partially decomposed. Decomposition then continues in the effluent line with the inherent acrid odors and clogging of downstream facilities.
Another disadvantage of the small single stage system is the absence of a "quiet zone," wherein suspended organic materials can settle from the effluent liquid and remain in the treatment system for a longer period of time in order to undergo further biodegradation. Agitation within the single stage system suspends the organic substances throughout the system, including the area near and around the discharge line, thereby inevitably causing some of the suspended solids to exit the system through the discharge line with the effluent liquid.
To overcome the problems associated with small single stage waste treatment systems, small stirrers have been added to improve the mixing within the system. However, the addition of stirrers require an increased amount of air to maintain biodegradation effectiveness and efficiency, and the pumps and stirring motors that are necessary to operate a stirrer generate noise and consume power. Furthermore, as with the single stage treatment systems, the effluent is often not fully treated by the time it reaches the discharge line, which can lead to offensive odors and clogging of downstream facilities. Still further, the absence of a "quiet zone" allows some of the suspended organic substances to exit the system before it is completely biodegraded.
Dual stage treatment systems have been introduced as an alternative solution to the problems inherent with single stage treatment systems. U.S. Pat. No. 5,061,369 to Romero, et al. discloses such a system. In Romero, the containerized domestic waste treatment system includes a liquid containing vessel divided into two chambers. Wastewater is fed into the first chamber where air is introduced to produce mixing and aerobic conditions. Once the wastewater is treated in the first chamber, it migrates into the second chamber where suspended solids are allowed to settle from the liquid before the treated wastewater exits the vessel. The dual stage treatment system is a marked improvement over single stage treatment systems. However, as in the single stage system, the oxygen used to maintain the activity level of the aerobic bacteria is limited to one pass through the system.
The apparatus of the present invention provides an energy efficient, low maintenance waste treatment system that thoroughly treats wastewater in multiple steps before the wastewater effluent is released to either the environment or to another downstream treatment facility. The present invention improves efficiency by producing turbulence and introducing oxygen in multiple stages in the waste treatment process, thereby reducing the amount of waste sludge and pollutants in the effluent stream, which in turn eliminates the offensive odors and clogging of downstream facilities.